Adductor spasmodic dysphonia (SD) is a serve and disabling voice disorder characterized by effortful, strained, staccato phonation and vocal fold spasms. Typically diagnosis is based on subjective evaluation of voice quality and visual observation of vocal fold behaviors. Because adductor SD is often accompanied by vocal tremor and behavioral responses (in particular vocal fold hyperfunction), accurate diagnosis and separation of co-occurring abnormal phonatory behaviors can be difficult. Identification of objective characteristics that separate adductor SD, vocal tremor, and behaviorally based hyperfunction is needed to ensure appropriate treatment discussions and monitor treatment effects. One aim of the present investigation is to differentiate adductor SD, vocal tremor, and behavioral hyperfunction based on a) between-group differences in phonatory air flow perturbations, phonatory air flow stoppages, and electroglottograph (EGG) vibratory stoppages; (b) within- speaker differences in the number of visible amplitude oscillations in the acoustic envelope for normal vs. high-pitched phonation and the distinctiveness of formants for normal vs. easy onset phonation. A second aim is to compare the differential sensitivity and reliability of selected aerodynamic, EGG< and acoustic measures to change in phonatory functioning following Botulinum toxin (BT) treatment of adductor SD. Individuals with adductor SD, vocal tremor, and behavioral hyperfunction will be identified after comprehensive voice evaluations. Subjects selection criteria will be stringent in a effort to compare adductor SD to "pure" cases of vocal tremor and behavioral hyperfunction. Phonatory air flow, intraoral air pressure, and EGG signals will be collect simultaneously as subjects repeat syllables. Acoustic signal will be recorded in a sound-treated booth while subjects perform speech tasks using normal, high-pitched, and easy-onset phonation. Measures derived from the air flow and EGG signals will be compared across groups. Within-individual differences in acoustic characteristics will compared across tasks. Changes in aerodynamic, EGG, and acoustic measures will be monitored over time for those individuals in the SD group who elect to receive BT treatment. Valid comparison of the relative effectiveness of treatment variations in the remediation of voice disorders is impeded by the lack of objective and quantitative measures that represent specific abnormal phonatory behaviors. The long-term objective of the present investigation is to use aerodynamic and EGG measures of vocal function to identify the most efficacious treatments for neurogenic voice disorders.